Distillation process for recovering anhydrous hydrogen fluoride



United States Patent 3,271,273 DISTILLATKON PROCESS FOR RECOVERING AN-HYDROUS HYDROGEN FLUORIDE Sherwood N. Fox, Stamford, Conn., and MartinB. Sherwin, Jackson Heights, N.Y., assignors to Halcon International,Inc., a corporation of Delaware Filed Feb. 13, 1963, Ser. No. 258,284Claims. (Cl. 203--12) This invention relates to processes for recoveringhydrogen fluoride from a mixture thereof with water, e.g., such amixture as the azeotropic composition (about 38% of the fluoride at 1atm.) by contacting the mixture with an oxygenated organic materialwhich is substantially insoluble in the aqueous mixture, whereby twophases are formed, each of which contains some of the hydrogen fluoride,separating the phases, and recovering hydrogen fluoride from the organicliquid. More particularly, it relates to such a process wherein theorganic material is cyclohexanol and it is recycled after strippinghydrogen fluoride therefrom, the aqueous phase being distilled to removewater and bring the mixture up to an azeotropic boiling concentration ofhydrogen fluoride, following which the azeotropic mixture is submittedto extraction by the cyclohexanol.

Hydrofluoric acid is a commercially important material and finds use inmany chemical processes, some of which produce an azeotropic boilingmixture thereof with water which is diflicult and costly to separate orbreak into its components. In particular, corrosion is often a problemin breaking this azeotrope. The art is confronted by the problem ofproviding convenient and economical methods for obtaining substantiallyanhydrous hydrogen fluoride from such mixtures.

The discoveries associated with the invention and relating to thesolution of the above problems, and the objects achieved in accordancewith the invention as set forth herein include the provision of:

A process for recovering anhydrous hydrogen fluoride which comprisesforming a two-phase mixture thereof with water and a water immiscibleoxygenated organic liquid, each phase containing some of the hydrogenfluoride, recovering hydrogen fluoride from the organic liquid phase,removing water from the aqueous phase to form an aqueous hydrofluoricacid azeotrope and returning the latter to the step of forming theseparate liquid phases;

Such a process wherein the dilute aqueous hydrofluoric acid isconcentrated to form aqueous hydrofluoric acid azeotrope and this iscontacted with the organic liquid to form the two phases, the liquidremaining after separation of hydrogen fluoride from the organic phasebeing returned to the contacting step;

Such a process wherein the hydrogen fluoride separated from the organicliquid phase contains some water and this is distilled to removehydrogen fluoride as overhead and leave a bottoms fraction which isaqueous hydrogen fluoride azeotrope and this is recycled to thecontacting step;

Such a process wherein the dilute aqueous phase is separated andconcentrated to produce aqueous hydrofluoric acid azeotrope and this isreturned to the contacting step;

Such a process wherein the organic liquid is cyclohexanol;

Such a process wherein the azeotrope is formed at 1 atm., and theseparated cyclohexanol phase contains up to about 20% of hydrogenfluoride and up to about 15% of water;

Such a process wherein the separated aqueous phase contains up to about37% hydrogen fluoride and up to about 3% of cyclohexanol at about 25 C.,and it is concentrated up to about 38% hydrogen fluoride and thenrecycled to the contacting step;

ice

Such a process wherein a cyclohexanol mixture containing water, hydrogenfluoride, and rearranged peroxidized cyclohexanol is stripped to removehydrogen fluoride and then extracted with water to remove hydrogenfluoride, leaving the bottoms fraction which is low in hydrogen fluorideand contains cyclohexanol together with the rearranged material, theextract being distilled;

Such a process wherein aqueous hydrofluoric acid is separated from theextract, following which the acid is distilled overhead, leavinghydrofluoric acid azeotrope which is recycled to the contacting step;

Such a process wherein the bottoms resulting from removal of hydrogenfluoride from the extract is contacted with cyclohexanol and theresulting two phases are separated;

Such a process wherein the aqueous phase is distilled to remove water asoverhead and leave a bottoms fraction which is aqueous hydrofluoric acidazeotrope and this is recycled to the contacting step;

Such a process wherein the cyclohexanol phase is distilled to removehydrogen fluoride as overhead and leave a bottoms fraction which iscyclohexanol and this is recycled to the contacting step;

And 'other objects which will be apparent as details or embodiments ofthe invention are set forth hereinafter.

In the accompanying drawing, FIGURES 1 and 2 are schematic flow diagramsof embodiments of the invention.

In order to indicate still more fully the nature of the presentinvention, the following examples of typical procedures are set forth inwhich parts and percents mean parts and percents by weights,respectively, unless otherwise indicated, it being understood that theseexamples are presented as illustrative only and they are not intended tolimit the scope of the invention.

Example 1 Referring to FIGURE 1, a dilute aqueous hydrofluoric acidmixture is passed via line 10 into azeotrope distillation column 12, andan overhead containing water is taken out via line 13, which may befurther distilled to recover any cyclohexanol therein (by means notshown). Recycled dilute aqueous hydrofluoric acid is passed via line 11into column 12 also. The bottoms from column 12 is approximately theaqueous hydrofluoric acid azeotrope and it is passed via line 14 toliquid-liquid contactor/separator 17 together with recycled cyclohexanolfrom line 16. Two separate liquid phases are formed. The cyclohexanolphase is passed via line 18 to hydrogen fluoride column 19, where ahydrogen fluoride stream is taken overhead and passed via line 20 tooptional final drying column 21, wherein essentially dry hydrogenflouride is separated as an overhead and it is removed 'via line 22. Theaqueous phase (which is a dilute hydrogen fluoride solution) is passedfrom contactor 17 via line 11 back to azeotrope distillation column 12.The bottoms from column 19 is predominantly cyclohexanol, and it isrecycled to the liquid contactor 17 via line 16. The bottoms fractionfrom column 21 is essentially an aqueous hydrofluoric acid azeotrope,and it is recycled to the contactor 17 via lines 15 and 14.

The dilute initial aqueous mixture is concentrated in column 12 byremoving water therefrom. Any cyclohexanol in the overhead may berecovered by decantation and, if necessary, by further distillation ofthe water stream in known manner.

The distillation in column 12 is carried out at 1 atrn. pressure andyields an azeotrope containing about 38% hydrogen fluoride.

This azeotrope bottoms fraction is sent to the contacting/separatingvessel 17 wherein cyclohexanol recycle amounting to about 5.6 times theweight of hydrogen fluoride in the azeotrope which is fed. Two liquidphases are formed and the hydrogen fluoride distributes itself betweenthese phases. The cyclohexanol phase contains about 75% cyclohexanol,12% hydrogen fluoride and 13% water. It is processed in column 19wherein hydrogen fluoride is distilled overhead, the cyclohexanol con-.

taining bottoms being returned to the vessel 17 to again serve as anextracting agent. The operation can be run so as to carry most of thewater with the bottoms. However, if a substantial amount of water iscarried with the hydrogen fluoride overhead it may be further processedin drying column 21 to take off anhydrous hydrogen fluoride as overheadand a bottoms fraction which is the aqueous hydrofluoric acid azeotrope,and this is recycled to the extraction step. The water phase from theextractor contains about 74% water, 23% hydrogen fluoride and 3%cyclohexanol. This is recycled to column 12 where water is removedoverhead.

In this way convenient and economical recovery of the hydrogen fluoridein essentially anhydrous form is achieved. It is important to regulatethe hydrogen fluoride distillation in column 19 to avoid or minimizedecomposition or chemical change of the cyclohexanol.

Any convenient contacting means may be used for the .two liquid phases,e.g., a simple mixer or a multi-stage reaction column. Other methods offorming the hydrogen fluoride-water-cyclohexanol mixture or likemixtures may be used; e.g., vapors containing these materials may bemixed and condensed to form the layers, which are then processed asdescribed herein, or a liquid cyclohexanol stream may be contacted withan aqueous hydrogen fluoride vapor.

Example 2 A reaction mixture containing cyclohexanol and hydrogenfluoride is produced by rearranging peroxidized cyclohexanol incyclohexanol solution containing about peroxy materials in the presenceof hydrogen fluoride. This process is set forth and claimed in pendingapplication Serial Number 183,031, filed March 28, 1962, now US. Patent3,234,212.

Referring to FIGURE 2 the rearrangement reaction eflluent may optionallybe passed via line 23 into column 24 and a portion of the hydrogenfluoride is removed therefrom in relatively dry form as an overhead vialine 26. The bottoms fraction or the eflluent is passed via line 25 tothe extractor column 26 and a bottoms fraction (low in acid) is passedvia line 31 to a neutralization vessel 45 where it is neutralized withan aqueous caustic mixture and is passed via line 46 to furtherprocessing to recover the cyclohexanol as well as other materialstherein. The recovered cyclohexanol may be returned to the initialreaction step.

The top fraction from column 47 is passed via line 27 to column 29 wherean aqueous fraction is separated overhead and passed via line 28 tovessel 47. Water is added via line 28a. The bottoms fraction (azeotrope)is passed via line 30 to decanter 33. The upper cyclohexanol phase ispassed via line 34 to cyclohexanol column 35 wherein hydrogen fluorideis taken olf as an overhead and passed via line 37 to drying column 38wherein anhydrous hydrogen fluoride is taken oif as an overhead vialines 39 and 26. The bottoms from column 35 is passed via lines 36 and30 to decanter 33. The aqueous hydrofluoric acid azeotrope bottomsfraction from column 38 is passed via lines 32 and 30 to the decanter33. The aqueous phase is passed from decanter 33 via lines 4-1 and 27 tocolumn 29 wherein water is removed as an overhead. The bottoms fractionfrom 29 is aqueous hydrofluoric acid azeotrope and it is passed via line30 to decanter 33 for further processing. Makeup cyclohexanol is addedvia line 36a.

The hydrogen fluoride overhead is further distilled torecover anhydroushydrogen fluoride which may be recycled to the arrangement reactionstep. The bottoms fraction is hydrogen fluoride azeotrope which isrecycled to the decanter for further processing.

From the economic viewpoint this is an advantageous operation especiallyfor producing such rearrangement derivatives in an economical manner. Aunique feature is use of one of the materials in the systems as anextraction solvent.

The process is also economical if stripper 24 is bypassed. In such acase, the composition in line 46 is about 73% cyclohexanol, about 10.5%water, and the remainder reaction product. The hydrofluoric acid contentis very low. The water extract in line 27 contains about 25% hydrogenfluoride, about 72% water and about 3% cyclohexanol.

In addition to cyclohexanol other oxygenated organic materials may heused in place of cyclohexanol as media. These include methyl isobutylketone, methyl isopropyl ketone, n-butanol, n-hexanol, and the like.

In view of the foregoing disclosures, variations and modificationsthereof will be apparent to one skilled in the art, and it is intendedto include within the invention all such variations and modificationsexcept as do not come within the scope of the appended claims.

What is claimed is:

1. A process for recovering anhydrous hydrogen fluoride by distillationwhich comprises forming a two phase mixture thereof with water and awater immiscible oxygenated organic liquid selected from the groupconsisting of n-butanol, methyl isopropyl ketone, methyl isobutylketone, n-hexanol, or cyclohexanol, each phase containing some of thehydrogen fluoride, recovering anhydrous hydrogen fluoride as overhead bydistillation from the organic liquid phase, removing water from theaqueous phase by distillation to form an aqueous hydrofluoric acidazeotrope as :bottoms and returning the latter to the step of formingthe separate liquid phases.

2. A process of claim 1 wherein the dilute aqueous hydrofluoric acid isconcentrated to form aqueous hydrofluoric acid azeotrope and this iscontacted with the organic liquid to form the two phases, the liquidremaining after separation of hydrogen fluoride from the organic phasebeing returned to the contacting step.

3. A process of claim 2 wherein the hydrogen fluoride separated from theorganic liquid phase contains some water and the separated hydrogenfluoride is distilled to remove hydrogen fluoride as overhead and leavea bottoms fraction which is aqueous hydrogen fluoride azeotrope and thisis recycled to the contacting step.

4. A process of claim 2 wherein the organic liquid is cyclohexanol andthe separated cyclohexanol phase contains hydrogen fluoride and water,said hydrogen fluoride being present in an amount up to about 20% byweight, said water being present in an amount up to about 15% by weight.

5. A process of claim 4 wherein the separated aqueous phase containshydrogen fluoride and cyclohexanol, the hydrogen fluoride being presentin an amount up to about 37% and the cyclohexanol being present in anamount up to about 3% by weight at about 25 C., and it is concentratedup to about 38% hydrogen fluoride and then recycled to the contactingstep.

'6. A process of claim 4 wherein cyclohexanol mixture containing water,hydrogen fluoride, and rearranged peroxidized cyclohexanol is strippedto remove anhydrous hydrogen fluoride and then extracted with water toremove hydrogen fluoride leaving the :bottoms fraction which is low inhydrogen fluoride and contains cyclohexanol together with the rearrangedmaterial, the extract being distilled.

7. A process of claim 6 wherein aqueous hydrofluoric acid is separatedfrom the extract, following which the acid is distilled overhead,leaving hydrofluoric acid azeotrope which is recycled to the contactingstep.

8. A process of claim 7 wherein the bottoms resulting from removal ofhydrogen fluoride from the extract is con tacted with cyclohexanol andthe resulting two phases are separated.

9. A process of claim '8 wherein the aqueous phase is.

References Cited by the Examiner UNITED STATES PATENTS 2,371,341 3/1945Matuszak 23153 X Hepp 20242 McKenna et al. 20260 X Frey 23153 X Carnell23153 X Shire 202--39.5 X

NORMAN YUDKOFF, Primary Examiner.

1 F. E. DRUMMOND, Assistant Examiner.

1. A PROCESS FOR RECOVERING ANHYDROUS HYDROGEN FLUORIDE BY DISTILLATIONWHICH COMPRISES FORMING A TWO PHASE MIXTURE THEREOF WITH WATER AND AWATER IMMISCIBLE OXYGENATED ORGANIC LIQUID SELECTED FROM THE GROUPCONSISTING OF N-BUTANOL, METHYL ISPROPYL KETONE, METHYL ISOBUTYL KETONE,N-HEXANOL, OR CYCLOHEXANOL, EACH PHASE CONTAINING SOME OF THE HYROGENFLUORIDE, RECOVERING ANHYDROUS HYDROGEN FLUORIDE AS OVERHEAD BYDISTILLATION FROM THE ORGANIC LIQIUID PHASE, REMOVING WATER FROM THEAQUEOUS PHASE BY DISTILLATION TO FORM AN AQUEOUS HYDROFLUORIC ACIDAZEOTROPE AS BOTTOMS AND RETURING THE LATTER TO THE STEP OF FORMING THESEPARATE LIQUID PHASES.